Revert CMake: Make most target symbols hidden by default

This reverts r362990 (git commit 374571301dc8e9bc9fdd1d70f86015de198673bd)

This was causing linker warnings on Darwin:

ld: warning: direct access in function 'llvm::initializeEvexToVexInstPassPass(llvm::PassRegistry&)'
from file '../../lib/libLLVMX86CodeGen.a(X86EvexToVex.cpp.o)' to global weak symbol
'void std::__1::__call_once_proxy<std::__1::tuple<void* (&)(llvm::PassRegistry&),
std::__1::reference_wrapper<llvm::PassRegistry>&&> >(void*)' from file '../../lib/libLLVMCore.a(Verifier.cpp.o)'
means the weak symbol cannot be overridden at runtime. This was likely caused by different translation
units being compiled with different visibility settings.

llvm-svn: 363028
diff --git a/llvm/lib/Target/WebAssembly/Disassembler/WebAssemblyDisassembler.cpp b/llvm/lib/Target/WebAssembly/Disassembler/WebAssemblyDisassembler.cpp
index 60e5549..f9bf3f8 100644
--- a/llvm/lib/Target/WebAssembly/Disassembler/WebAssemblyDisassembler.cpp
+++ b/llvm/lib/Target/WebAssembly/Disassembler/WebAssemblyDisassembler.cpp
@@ -65,7 +65,7 @@
   return new WebAssemblyDisassembler(STI, Ctx, std::move(MCII));
 }
 
-extern "C" LLVM_EXTERNAL_VISIBILITY void LLVMInitializeWebAssemblyDisassembler() {
+extern "C" void LLVMInitializeWebAssemblyDisassembler() {
   // Register the disassembler for each target.
   TargetRegistry::RegisterMCDisassembler(getTheWebAssemblyTarget32(),
                                          createWebAssemblyDisassembler);